But I think everyone else knew the difference between feeding and chambering, except the OP. Since there were magazine change reccomendations and short stroking.... But no one paid attention to the ghost round being ejected.

__________________
Freedom's just a word. If I'm gonna die for a word, my word is jello...

I used a Spikes mid-length upper and a Knights Armament mid-length upper in my testing. I put the uppers on my lower and everything functioned perfectly. I put my YHM upper on both Spikes and KAC lowers and failed on both.

I interchanged the buffers just to be thorough but there was no difference.

Here's a weird issue that popped up. I pulled the BCG out of the other 2 uppers and tried to put them in my YHM upper and they would not go in...but the BCG from my YHM upper would fit fine into the other 2 uppers. All 3 BCGs are the standard M-16 style and look identical. I had several people try to do this and everyone is stumped. Weird.

.....or, the bolt is catching the case just forward of the rim and starting to strip it partially out of the mag before finally slipping off leaving the bolt jammed against the partially chambered round.

I took the upper to my friend's house the other night. He's a certified AR-15 gunsmith. We did some investigation on the whole rifle just to make sure everything (including my lower) was perfect and aligned and it looks like the gas block wasn't seated over the hole. Measurements showed that the gas block was misaligned by .050 and only 1/4 of the hole in the barrel was centered with the hole for the gas block, and that was probably limiting the amount of gas being pushed through the gas tube. We reseated the gas block .050 closer (yes, that's point zero five on his digital caliper) to the end of the barrel.

He has no explanation for the previously discussed issue regarding my friends' BCGs not fitting. He took several BCGs from his stash and all fit perfectly. Just weird. Oh well, no biggie on that.

I will be testing this weekend to check functionality.

On a side note, the gun shop owner emailed me last night to apologize for the delay and offered to replace the upper at no charge. Makes me feel at least a little better about reliability/accountability of the store.

A blocked gas port on a lower-than-carbine pressured upper? That'll do it for sure. Even an adjustable gas block won't save you if it's not on there properly

I've been following this thread intently as well, since I've just built my first build, which consists of a rifle length gas system on a carbine-based lower. CTS hit the nail on the head - I've done a considerable amount of perusing on the net, and there seems to be a significant misconception about buffer weights and the purpose of adding mass to the system and when it is (and isn't) appropriate. Thanks for posting this, pturner- but now you've got me all worried about how mine will do

The lower works perfectly with other uppers so it isn't an issue with the lower.

The gas tube is the proper length and isn't blocked; we checked that first.

Tested the AR this weekend. It functioned ok (not as smooth as my last AR) using 5.56...but same issue (FTF) using brass .223. Something I didn't think about was that the 5.56 used was in a different PMAG than the .223 so I will have to next try swapping out different PMAGS with ammunition.

The front gas block is the YHM-9394...looks to be pretty standard for the AR

If my next tests don't come up with any answers, I'm sending the complete upper back to be replaced

If it wasn't lined up with the port, then I can see why you had a problem.

If 5.56 worked, but just barely, then I could see it causing an issue with lower pressure 223.

As far as my upper problem... I put in an H2 buffer and it lessened but didn't eliminate the problem. Talked to customer support and working on getting a replacement. The ball is rolling, just need to send them a copy of the receipt.

I think you have a tight cut chamber (probably under spec) or your gas tube is misaligned. If the bolt locks back on the last (or only) round and it's going back far enough to strip a round I severely doubt it's a gas/buffer issue. Check your bcg and gas tube for dents, notches, etc that would show misalignment. Will brass rounds chamber if you release the bolt over a loaded mag after shooting steel?

Again, we run into some lingo issues. A BCG is a Bolt Carrier Group. The actual bolt fits INTO the BCG. So did the BCG not fit, or did the bolt(s) not fit into the chamber?

Either way I think your chamber is out of spec. From the information you've given that seems the most likely culprit. Can you push brass rounds in your chamber? They should slide in easily with no pressure or even fall in with the upper vertical.

Might just be a sloppy chamber. If it's unlined and not nitrided you could try the 870 chamber trick, but since it's giving you issues, I'd take the store's offer and trade it out.

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Freedom's just a word. If I'm gonna die for a word, my word is jello...

It's on the tight side of spec, but not too tight, measured by comparing unfired factory rounds to fired casings using a cartridge headspace gage. My other rifle has a SS barrel with a slightly tighter chamber. Maybe one thou, maybe one and a half, very little expapansion in fired brass. I checked the gas tube for alignment to my gas key to ensure no abnormal wear. The bolt locks up without undo force.

Its PSA's CHF barrel from FN... I would hope they made a barrel properly, but things happen I guess.

Gas tube is aligned...BCG slides over it just fine in the chamber...and now the gas block is aligned correctly over the hole in the barrel

Will brass rounds chamber if you release the bolt over a loaded mag after shooting steel? yes

Can you push brass rounds in your chamber? They should slide in easily with no pressure or even fall in with the upper vertical. Answer is yes, they slide in easily.

So did the BCG not fit, or did the bolt(s) not fit into the chamber? My friends' Spikes and KAC BCGs from my original post did not fit. But that seems to be an error on my part because my gunsmith friend put his Spikes BCG in and it fit fine.
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Will be testing in the next few evenings different rounds loaded into different PMAGs.

Gas block properly aligned over the hole in the barrel. Gas tube is clean and aligns with the BCG. Buffer is standard buffer (not the ST-T2/3 that I had before).

Where things currently stand: pull back the handle...insert loaded PMAG...release...fire AR...ejects just fine...but next round gets caught semi-sideways by the BCG and doesn't get chambered

Seems you have given your upper the best chance at functioning that you can. So hopefully the testing will go well. If it works well this time, you may be able to run the heavier buffer just as well. Might feel better with the added weight I the buffer slowing down recoil a bit. But if not, full functioning with how you have it set up now will be good to go as well.

Where things currently stand: pull back the handle...insert loaded PMAG...release...fire AR...ejects just fine...but next round gets caught semi-sideways by the BCG and doesn't get chambered

I have not read every post in this thread, but your problem is interesting for sure.

Here's a couple of questions to verify:

1. Does it always lock back on the last round using 5.56 ammo only?
2. Do the problems happen on 223 ammo?
3. How much lube do you have on the BCG, and how many total round count on the rifle now?
4. Have you tried duplicating the issue with another BCG like the Spikes?

--

Try this again and see if you can isolate the issue:
1. Use only factory loaded 5.56NATO ammo for each test.
2. Use a new magazine preferably a Pmag or any mag that is known to be reliable.
3. Do the one-round in the mag test for at least 10x to see if it locks back every time.
4. Then load 2rounds in the mag and see if it still works or does not feed on 5.56 ammo. If you get FTF's, then you are definitely shortstroking from the upper.
5. Check that the gas block and gas tube is tight and not working itself loose.

My only other thoughts is that it could be your BCG. What exactly is the BCG and what brand??

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